Marmosops incanus is dark brownish-gray dorsally with craemy-white underparts. The pelage is long and very soft in young animals. Adults are the same color as young, but have a distinctive, short-haired pelage. These age-related pelage differences were thought to be winter (long pelage) and summer (short pelage) coats. A lateral band of gray-based hairs separates the dorsum from the venter. The eye rings are dark, prominent, and extend onto the snout. The dorsal side of the tail is fuscous, with the last 2/3 inch or so whitish. Males and females are markedly dimorphic, with males reaching much larger sizes. Adult males range in total body length approximately 11-17 inches and weigh 1-6 ounces. Females range in total body length approximately 10-14 inches and weigh 1-3 ounces. The tail is long, approximately 1.5 times the combined head and body length. The ears are large, averaging more than 1 inch in both sexes. The distinctive adult pelage is also dimorphic. In adult males the hairs of the throat and shoulder regions are replaced by short hairs, much stiffer and coarser than in young animals. In females the entire dorsal pelage is replaced by short hairs, but these are soft as in the juveniles.

The dorsal pelage color varies geographically. Individuals from the semi-decidous and gallery forest in cerrado and caatinga habitats are markedly paler gray than those from the wet coastal habitats. Oliveira et al. (1992); Mustrangi and Patton (1997).

Marmosops incanus inhabits the humid forest from sea level to 800 m along the coast as well on continental islands. It is also present in the drier, semi-deciduous forest, extending its distribution inland of the coastal mountains onto the Brazilian plateau where it is present at much higher elevations (up to1300 m). Marmosops incanus is also present in gallery forest in the cerrado and caatinga domains adjacent to the Atlantic forest (Mustrangi and Patton 1997).

Biomes: tropical rainforest, tropical deciduous forest, tropical scrub forest

Neotropical: Marmosops incanus is widely distributed along the east coast of Brazil, from about 10 to 25 degrees south latitude. (Emmons and Feer (1990); Mustrangi and Patton (1997).

This species has an interesting life cycle. Breeding occurs during three months (Sept.-Dec.), following which all adult males evidently die, so that none exists in the following seven months (Feb.-Aug.). Adult females survive through May, and then die, so that none are present from June to August when the population includes only young of the year. Males thus have a lifespan of about a year, and females of a year and a half. At birth, the young are exceptionally altricial. There may be geographic variation in the months when breeding occurs, usually during the rainy season. The limited breeding season shown by M. incanus indicates that the female are monoestric and that the estrous cycle is short. Each individual participates in only one reproductive season during its lifetime. However, at least two reproductive periods in the year are found in one population, a major one from Oct. to Dec. and a second, in which fewer animals participate, ocurring from March to May. Tribe (1990); Emmons and Feer (1990); Lorini et al. (1994).

The gray slender mouse opossum appears highly insectivorous, feeding mostly on insects belonging to the orders Coleoptera and Orthoptera (de Fonseca and Kierulff, 1989).

Not much is known about the behavior of the gray slender mouse opossum. It can be characterized as an scansorial species, that is, it uses terrestrial and arboreal resources. Males appear to be more sedentary than females. de Fonseca and Kierulff (1989).

Until recently the genus Marmosops was grouped in the genus Marmosa, and the gray slender mouse opossum was known as Marmosa incana. Recents morphometrics and DNA variation analyses showed that M. incanus is sympatric with another slender mouse opossum, M. paulensis (Gardner and Creighton 1989; Mustrangi and Patton 1997).

A. B. de Fonseca & M. C. Kierulff. 1989.
Biology and natural history of Brazilian Atlantic forest small mammals. Bulletin of the Florida State Museum, Biological Series 34:99-152.

J. A. de Oliveira, M. L. Lorini, & V. G. Persson. 1992.
Pelage variation in Marmosa incana (Didelphidae, Marsupialia) with notes on taxonomy. Zeitchrift Fuer Saeugetierkunde 57:129-136.

Louise H. Emmons & Francois Feer. 1990.
Neotropical Rainforest Mammals: A Field Guide. University of Chicago Press, Chicago, IL.

A. L. Gardner & G. K. Creighton. 1989.
A new generic name for Tate's (1933) microtarsus group of South American mouse opossums (Marsupialia: Didelphidae). Proceedings of the Biological Society of Washington 102:3-7.

M. L. Lorini, J. A. de Oliveira, & V. G. Perssom. 1994.
Annual age structure and reproductive patterns in Marmosa incana (Lund, 1841) (Didelphidae, Marsupialia). Zeitchrift Fuer Saeugetierkunde 59:65-73.

M. A. Mustrangi & J. L. Patton. 1997.
Phylogeography and systematics of the Slender Mouse Opossum Marmosops (Marsupialia, Didelphidae). University of California Publications, Zoology 130:1-86.

C. J. Tribe. 1990.
Dental age classes in Marmosa incana and other didelphoids. Journal of Mammology 71:566-569.